[Towertalk] Really dumb question on coax

[Michael Tope]

Bruce,

The difference neglecting the additional connector losses is 0.76 dB.
At 1500 watts, the difference in power delivered would be 174 watts.
The losses associated with the additional splice will be insignifcant
(<< 0.05dB), so as long as you are confident that your splices will be
reliable, the LMR600/9913 combination will give you an ~20%
advantage in power delivered to the antenna. Not a huge difference,
but when averaged over many thousands of contacts, it can, in my
opinion, be significant.  (the extra barrel connector and two PL-259s
will be much cheaper than the cost difference between a Heath
SB-220 and an Ameritron AL-1500).

With regard to failure rate of splices. Consider the number of outdoor
PL-259/SO-239 junctions, N in your station and the current rate of
failure. The additional splice will increase your failure rate by
Delta_FR = [((N+2)/N)-1]*100%. If you already have 50 junctions,
in theory your failure rate will only go up by 4% when you add the extra
splice. If you average 1 failure per year, the additional splice will on
average raise the failure rate to 1.04 connectors per year (that's one
additional junction failure every 25 years). Not a bad price to pay
for 0.75 dB (think how much longer you would have to make the
boom on your antenna to get  that 0.75dB of extra gain).

73 de Mike,
W4EF................................................................

----- Original Message -----
From: "Bruce Makas" <k1my@msn.com>
To: "Towertalk submital" <towertalk@contesting.com>
Sent: Tuesday, May 28, 2002 3:54 PM
Subject: [Towertalk] Really dumb question on coax


> One of my towers is 270 feet from the entry point (where all the switching
> and grounding takes place) to the house. I have a 200 foot length of
LMR600
> (loss of 0.42 db per 100ft @ 30 mhz) and lots of Beldon 9913FX (0.8 db
loss
> per 100 ft).
>
> My question is whether I'm better off using 270 feet of the Beldon or 200
> feet of the LMR and 70 feet of the Beldon connected with PL259's and a
> barrel connector.
>
> 270 x 0.8 = 2.16 db loss
> 200 x .42 + 70 x .8 = 1.40 db plus loss of connectors
>
> I know that I can make a watertight joint so feedline loss should be my
only
> concern. I know that it is close and that I probably can't tell the
> difference but which way is actually better?
>
> Thanks,  Bruce K1MY
>
>
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